My 2007 XJR has recently twice come up with a CEL and using the Torque Pro app on my tablet it turns out to be the (apparently common) P0430 fault which relates to catalytic converter inefficiency in Bank 2. The strange thing is that the car has only done 41000 km. I tried graphing the O2 sensor outputs but the app would only display "sensor 2" on each bank. You would think sensor 2 would be the post-cat converter sensor but the output was all over the place while revving so I suspect it is actually the pre-cat sensor. The outputs from each Bank are symmetrical most of the time but every so often one is quite different. To add some confusion the one that looks wrong (not responding to my revving) appears to be the one for Bank 1.

I'd be tempted to just cancel the fault each time it occurs but I have some Nameless Performance sports cats being shipped and having a pre-existing fault may confuse things when the new cats are installed.

Should I get this issue sorted before installing the new cats? Or replace the O2 sensors at the same time as replacing the cats?

Cheers,

Steve

 

If you are changing the cats, I would think that will solve the cat innefficiency code. When I look at my O2 sensor outputs on the scanner they also look random and wild. I think it's because the sample rate of the communication bus to the reader is much slower than the cycle rate of the O2 sensors. Sensors cycle as they work, so if you randomly sample the output it will look like it is bouncing all over the place.

Once the new cats are installed, simply clearing the old code should be all it takes. Even if you don't clear it, it will not be a problem. The ECM just looks at what is happening now...it saves the previous code, but that will not affect how it operates with the cat replaced.

John

 

Thanks cjd for your help. Yes, I did wonder if the O2 sensor traces were unreliable due to a slow OBD2 reader... I've noticed that there is a delay in other readings as well (like revs etc).

The reason that I wonder about the O2 sensors is that the cats have only done 41000km (25k miles), so I don't think the cats should be stuffed yet. The reason I am replacing them is just to get more performance with higher flowing ones, I had actually ordered these before I got the first P0430 code.

 

I am with you on that, they should not go bad that early. You never know, though, one tank of gas from a station that put the wrong fuel in one of their tanks could do it...although you would think even that would affect both cats??

Be sure to keep us up to date once you swap out the new cats...I'm curious to hear how they work!

John